1. Field of the Invention
The invention relates to a method for stabilizing a power supply device or a power supply network against reactive load fluctuations of at least one electric load having a variable reactive load, and to a reactive power compensation device.
2. Discussion of Background
U.S. Pat. No. 5,155,740 discloses a flicker compensation device for DC arc furnaces, in which reactive power control is performed only as a function of the detected reactive power of the arc furnace.
In the case of this compensation, no account is taken of currents in filter branches and auxiliary equipments. In the case of small electrode currents, the reactive power of the furnace can become too low. When there are permanently installed capacitor banks, this leads to overcompensation, which is frequently not accepted by power supply companies.
EP-A1-0 498 239 discloses controlling an arc furnace by means of DC feed having 2 control loops. A current controller ensures a constant current corresponding to a prescribed desired current value. An electrode control loop influences the position of the electrode, and thus the arc length. In the event of lengthening of the arc, the current controller must increase the voltage or drive the rectifier in such a way that the current remains constant. However, this is only possible as long as there is a voltage reserve. Controlling the electrode is performed by means of an adaptable DC voltage controller. The arc voltage, which is fed via a damping element to a comparator or summer, serves as the actual DC voltage value. The desired DC voltage value must be calculated in each case taking account of the transformer voltage stage and of the electrode current for each working point. Firstly, a limiter is used to impose a limit in accordance with the transformer stage of the power converter transformer, and thus with the possible voltage range of the power converter, in such a way that the power converter is operated in a steady-state fashion at most just below the rectifier limit. The desired value is fed in a smoothed fashion to the summer, in order in the event of sudden changes in the desired voltage value not to obtain any overshooting of the actual value, which could effect interrupting of the arc. Nothing is stated there about compensating reactive power fluctuations.